Analysis by Chris Cillizza, CNN Editor-at-large

(CNN) -- Just 24 hours removed from arguably his best day as President, Donald Trump picked a political fight he cannot win.

On Monday night, the Trump administration announced that it now supports a ruling from a Texas judge that would invalidate the entire Affordable Care Act -- aka Obamacare -- a move that almost certainly will push the fight over how health care is delivered in this country to the Supreme Court.

"The Department of Justice has determined that the district court's comprehensive opinion came to the correct conclusion and will support it on appeal," said Kerri Kupec, a spokesperson for the Justice Department.

That decision, which caught even many Trump allies by surprise, again thrusts the health care issue to the center of the political debate, and virtually ensures that the 2020 election -- like the 2018, 2016, 2014, 2012 and 2010 elections before it -- will turn on the ACA.

It's a baffling move for Trump, who spent most of Monday basking in the glow of a series of conclusions, according to Attorney General Bill Barr, in special counsel Robert Mueller's report that were about as favorable as the President could have hoped for: That the special counsel did not establish that anyone in Trump's campaign conspired with the Russian government in 2016 election interference, and that there was not sufficient evidence for Barr to establish an obstruction of justice charge against the President.

Switching the spotlight of the national debate from Russia to health care so quickly would be risky under any circumstances but is particularly problematic given that a) the past five elections have shown that people care deeply about and vote on the issue of health care and b) getting rid of Obamacare is not a broadly popular view with the American public.

In a February, Kaiser Family Foundation poll on the ACA, 50% approved of it while 37% disapproved. In fact, since President Barack Obama left office in January 2017, his signature legislative accomplishment -- and the one that bears his name -- has grown steadily more popular. Since May 2017, according to Kaiser data, more people have approved of Obamacare than disapprove -- a sea change from most of the previous five years, when the law was consistently underwater in terms of approval. Many of the provisions of the law that have long been the most popular -- allowing kids to stay on their parents' insurance through age 26, no discrimination by insurance companies because of a patient's preexisting conditions -- remain in effect. The least popular provision -- the individual mandate that forced everyone in the country to have some sort of health care -- was effectively eliminated by congressional Republicans (and Trump) in their 2017 tax law.

Those numbers explain why House Democrats ran hundreds upon hundreds of TV ads during the 2018 midterm elections making the case that Republicans, if they had their way, would have eliminated Obamacare altogether. "Republicans will do absolutely anything to divert attention away from their votes to take away Americans' health care," then House Minority Leader Nancy Pelosi (D-California) said in the days leading up to the midterms. And, following Democrats' takeover of the House in 2018, Pelosi was just as clear; "Health care was on the ballot, and health care won," she said.

The data back up Pelosi's position. More than 4 in 10 voters in 2018 said that health care was their top priority in the election, according to exit polling. Democrats won those health care voters by 52 points. 52!

That massive edge for Democrats reflects just how much the political landscape has tilted on the issue over the past decade. Opposition to what many conservatives viewed was a massive government overreach into what should be best handled by the private market led to Republicans winning control of the House in the 2010 midterms. By 2012, public opinion on the law had stabilized somewhat and Obama was re-elected relatively easily. Two years later, however, amid implementation problems and the famous/infamous backtracking on "if you like your health care plan, you can keep it," Republicans again ran on their opposition to the ACA and made more seat gains in Congress. In the 2016 presidential election, Trump ran explicitly on a plan to repeal and replace the ACA. By 2018, Democrats were able to capitalize on the fact that House Republicans had approved a repeal and replace package that never became law because it failed in a late-night vote in the Senate.

Trump's decision to pick this fight at this moment is, therefore, tough to understand. There's no question that his base hates Obamacare and would like to see it gone. And that he believes that at least part of his 2016 victory -- and maybe his chances at re-election in 2020 -- hinge on him making good on removing the most visible footprint of his predecessor. At rally after rally during the 2018 campaign, Trump re-told the story of John McCain's decision to vote against the so-called "skinny repeal" of Obamacare, a line that always drew boos and jeers directed at the late Arizona senator from the crowd.

Trump has spent the entire first two years of his presidency playing to his hardcore base -- and, seen through that lens, the decision to re-litigate the ACA fight makes some sense. But Trump won't win a second term solely on the strength of his base. And by picking the Obamacare scab, Trump is energizing and inflaming Democrats and many independents. And that is a major political mistake.